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Collision avoidance for moving robotic limbs

  1. Feb 13, 2019 at 11:45 AM #1
    Let's say you have a low force hobby robotic arm that's supposed to perform a certain movement, but it should stop if there is an object in the way. What sort of sensors/solutions exist for this?

    I've considered force sensors but I'm not sure if that's the best idea since I'd have to place many sensors all over the arm.

    Any suggestions are welcome, thanks in advance.
  2. jcsd
  3. Feb 13, 2019 at 12:14 PM #2
    You could detect current changes in your actuators that imply a load increase from a collision. Mind you that needs a collision to be able to detect it, so not much good at the "avoiding" part...

    If actual avoidance is the goal something like ultrasonic or optical would be the first ones that spring to mind.
  4. Feb 13, 2019 at 12:30 PM #3
    Avoidance would be nice but not strictly necessary. Your first suggestion with current changes might just work. Thanks!
  5. Feb 13, 2019 at 12:47 PM #4


    Staff: Mentor

    Passive Infrared Sensors (PIR) are common and inexpensive. But I don't think they are meant for close-in range.

    You should specify your required range. Maximum range an object can be detected. Minimum distance between the arm and the object.
  6. Feb 13, 2019 at 12:56 PM #5
    I'm fairly flexible on the range, something like 5cm and up would work.
    I'm not super picky with the precision, I just need something I can use and then modify the system around that capability.
  7. Feb 13, 2019 at 1:09 PM #6


    Staff: Mentor

  8. Feb 13, 2019 at 1:26 PM #7
    Super! What sensor would work for things such as walls and other solid non living objects?
  9. Feb 13, 2019 at 2:15 PM #8


    Staff: Mentor

  10. Feb 13, 2019 at 4:59 PM #9
  11. Feb 14, 2019 at 1:42 PM #10


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    Staff: Mentor

    My first thought would be to use an IR Reflective type sensor to detect when the detector is moving close to some object. I would use IR to avoid lots of extraneous light coming out of the robot arm parts, and I would modulate the IR transmissions (and demodulate the RX signals) to improve noise immunity. This page from Digikey (of all places) is a pretty good tutorial on the different kinds of IR sensors and their uses:


  12. Feb 14, 2019 at 7:55 PM #11
    Bump strips ?

    Long ago, I built a free-roaming robot from an electronics magazine's series. IIRC, it had both drive-load sensing, using a hand-wound 'current' coil over a reed relay for L & R motors, and a bump strip at front. That was a 'curly bracket' of half-inch phosphor-bronze spring, plus a couple of 'whiskers' behind which 'grounded' to the back of spring upon impact. Which, incidentally, also told the robot which way to reverse...

    I later 'rolled my own' using a toy tank chassis, the spring recurved between front idlers...

    Now, my wife's 'Big Name' chair-lift has a slim 'bump bar' in sides of the foot-rest, plus internal motor-load monitoring...

    IIRC, there are many off-the-shelf types of bump strip for guarding industrial machinery and power-assisted doors. Whatever, remember it has to work much faster than your servo drivers cook, lest their 'magic smoke' escape. Exploding power MOSFETS are NOT funny...
  13. Feb 16, 2019 at 3:49 AM #12


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    That's what I was leaning towards - a contact sensor.
    The blue lines are wires that are connected to a switch, normally open, that close when the wire hits an object.
    What the software does with the signal is up to the user - stop the motor, go in reverse, go slow, activate the load sensing routine, etc
    The ring would ne connected to multiple switches for 360 degree contact sensing.
    A ring could be put on the end of the wires also for 360 degrees..

    I imagine contact sensing would be simpler to set up firstly, to flesh out the routines that one might need, and then move up to other sensors after this is down pat .

    Patent #000000001
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